Potentially harmful blue-green algae found at Lethbridge's Henderson Lake

Alberta Health Services says blue-green algae can cause skin irritation, rash, sore eyes, sore throats, nausea, vomiting and diarrhea in people that come into contact with it. (File)

The City of Lethbridge is warning residents to avoid the water at Henderson Lake due to the presence of blue-green algae.

Blue-green algae, also known as cyanobacteria, is naturally occurring but can potentially produce toxins that are harmful to people and pets.

It looks like scum, grass clippings, fuzz or globs on the surface of water and can be blue-green, greenish-brown, brown and/or pinkish-red in colour. It often smells musty or grassy.

Access to the boat launch and docks at Henderson Lake is currently closed because of the algae.

Those visiting the area are advised against coming into contact with thelake's water or letting pets swim or wade in tit, as exposure to the bacteria may be fatal to pets.

"The prolonged warm weather with little wind for mechanical mixing is likely the cause of this late season bloom," said the City of Lethbridge in a Tuesday news release.

"The species was confirmed today with lab testing and a conversation with Lethbridge College’s water department."

There are no treatments to rid bodies of water of cyanobacteria blooms once they are underway.

People who come in contact with visible blue-green algae or who ingest water containing blue-green algae may experience skin irritation, rash, sore throat, sore red eyes, swollen lips, fever, nausea and vomiting and/or diarrhea.

Symptoms usually appear within one to three hours and resolve in one to two days.